1. Field of the Invention
The present invention relates to an ink jet recording head that records by discharging recording droplets to a recording medium by use of the ink jet recording method for the adhesion thereof to it. The invention also relates to a method of manufacture therefor. More particularly, it relates to an ink jet recording head for discharging fine recording droplets stably at higher speeds in order to obtain images recorded in higher precision, and a method of manufacture therefor as well.
2. Related Background Art
With the ink jet recording head, recording (printing) is made by discharging the ink that serves as recording liquid from the fine discharge ports (orifices) as flying droplets which adhere to a recording medium (a paper recording sheet or the like). To structure the ink discharge unit of the ink jet recording head, there are laminated a resin member on a substrate provided with a plurality of discharge energy generating elements and lead electrodes on it in order to form a plurality of grooves that serve as ink liquid flow paths and a groove that serves as a common liquid chamber communicated with the plurality of liquid flow paths. To the resin member formed on this substrate, the glass ceiling plate provided with an ink supply opening is bonded to cover all the grooves for the formation of the liquid flow paths and the common liquid chamber.
In recent years, the above-mentioned glass ceiling plate is omitted, while the ink supply opening is added to the grooves that serve as the liquid flow paths and the common liquid chamber. Then, the resin ceiling plate is formed by means of injection molding or the like together with the orifice plate having discharge ports formed therefor. Such resin ceiling plate and the substrate provided with the discharge energy generating elements are bonded through an elastic member so that each of the discharge energy generating elements is fittingly arranged for each of the flow path grooves on the ceiling plate. In this manner, there has been developed an ink jet recording head formed by bonding the resin ceiling plate and the substrate.
FIG. 9 is a perspective view which shows the principal part of the ink jet recording head formed by bonding such resin ceiling plate and substrate. In FIG. 9, the second substrate that serves as the resin ceiling plate is partly broken for representation. As shown in FIG. 9, a plurality of discharge energy generating elements 701 for discharging ink are arranged in parallel for the first substrate 702. On the other hand, the resin second substrate 710 is structured by the ceiling plate portion 711 and the orifice plate portion 708. Here, the ceiling unit 711 is configured in such a manner that it is connected vertically with one surface of the orifice plate portion 708. On one surface of the ceiling plate portion 711, the ink supply opening 709 is arranged. Here, a hole extended from the ink supply opening 709 penetrates the ceiling plate portion 711 vertically. On the other surface of the ceiling plate portion 711, where the hole form the ink supply opening 709 is open, there are arranged a groove extendedly in parallel with the orifice plate portion 708 to serve as the common liquid chamber to retain ink temporarily, and a plurality of grooves communicated with the common liquid chamber 706 to serve as liquid flow paths which are extended on straight lines from the common liquid chamber 706 in the direction toward the orifice plate portion 708. On the leading edge portion of the orifice plate portion 708 to which the plurality of liquid flow paths 707 are extended, the holes are arranged to penetrate the orifice plate portion 708. Through these holes, the liquid flow paths 707 are communicated with the outside. These through holes on the orifice plate portion 708 become the ink discharge ports 705. The surface of the second substrate 710, where the grooves are provided for the common liquid chamber 706 and the liquid flow paths 707, and the surface of the first substrate 702, where the discharge energy generating elements 701 are formed, are arranged to face each other so that the discharge energy generating elements 701 are positioned with the corresponding liquid flow paths 707. Then, these surfaces are pressed with an elastic material (not shown) between them to bond the first substrate 702 and the second substrate 710 for the formation of the common liquid chamber 706 and the liquid flow paths 707. The first substrate 702 bonded together with the second substrate 710, and the wiring substrate 703, which is provided with driving circuits installed thereon to generate electric signals to be transmitted to the first substrate 702, are fixed on the base plate 704, thus forming the principal part 714 of the head.
Now, with the principal part 714 of the ink jet recording head shown in FIG. 9, an ink jet recording head is fabricated as represented in FIG. 10. Here, the head principal part 714 is integrally formed by the injection molding together with the grooves that become liquid flow paths 707 to supply ink (recording liquid) to the head principal part 714, the ceiling plate portion 711 provided with the ink supply opening 709, and the orifice plate portion 708 as shown in FIG. 10. Then, a part of the orifice plate portion 709, which is the plate portion of the integrally formed resin member, prepared for the formation of the discharge ports 705, is irradiated by excimer laser from the common liquid chamber side to from them. In this manner, the second substrate 710 is produced.
Now, with reference to FIGS. 11A to 11C, the description will be made of the operation of the ink jet recording head structured as described above. The interior of the common liquid chamber 706 is filled with ink supplied from the ink supply opening 709. The interior of each of the liquid flow paths 707 is also filled with the ink that has flown into it from the common liquid chamber 706. When each of the discharge energy generating elements 701 is supplied with electric power, thermal energy is generated as discharge energy. With the thermal energy thus generated, film boiling is created in ink on each of the discharge energy generating elements 701, hence air bubbles being formed in the liquid flow paths, respectively. By the development of each air bubble, ink that resides between the corresponding discharge energy generating element 701 and discharge port 705 is pressed toward the discharge port 705. Then ink is discharged from the discharge port 705.
However, the progress of recording technologies, particularly the progress in making the precision of recorded images more precise, is remarkable in recent years. As a result, it has been demanded to make recorded images highly precise not only in the conventional resolutions of from 360.times.360 dpi (dot per inch) and 600.times.600 dpi to 720.times.720 dpi, but also, in the extremely high resolution of 1200.times.600 dpi or the like.
In order to materialize highly precise images recorded by use of an ink jet recording head, it is necessary to make the recording droplets extremely small when discharged from each of the discharge ports. However, there is a problem encountered that it is very difficult to discharge the extremely fine recording droplets stably at high speeds by use of the ink jet recording head produced by the conventional art. Now, hereunder, such problem will be discussed with reference to FIGS. 11A to 11C which illustrate the conventional techniques.
In other words, there is a need for making the diameter of each discharge port smaller in order to make each recording droplet a small one. Then, when the discharge port is made smaller, the residing region of the fluid resistance component (the step 730 in FIGS. 11A to 11C) becomes larger in the portion that connects the discharge port with the liquid flow path. As a result, due to the presence of this fluid resistance component, the amount of reflection is increased against the discharge pressure waves when bubble is generated by the heater. This increased reflection disturbs the ink flow at the time of refilling. A flow disturbance of the kind tends to result in lowering the refilling frequency. Meanwhile, the enhancement of resolution as described earlier necessitates the increased numbers of recording droplets inevitably. Therefore, in order to secure the same printing speeds as those conventionally available, it is necessary to obtain a sufficient discharge frequency. This in turn requires the enhancement of refilling frequency.
In this respect, if each of the discharge energy generating elements should be driven at higher speeds for discharging smaller droplets just by making the diameter of each discharge port smaller, the refilling capability tends to become insufficient eventually, hence making it hardly attainable to obtain the discharge characteristics in good condition as desired.
Also, as another method for making recording droplets small ones, it is practiced to make the heater power smaller. However, although this method produces a favorable effect on the enhancement of the refilling frequency, it tends to results not only in reducing the discharge amount of recording droplets, but in reducing the discharge speeds. This tendency may invite the twisted flight of recording droplets or the like, and from the practical point of view, a method of the kind can hardly be regarded as a desirable one.
Further, it may be possible to enhance the refilling speeds by making the volume larger in the liquid flow paths and the discharge ports on the discharge port side than the energy generating device side, because this arrangement makes the amount of displacement smaller for each meniscus. However, if such volume is made larger just by shifting the energy generating devices to the liquid chamber side, the discharge efficiency of recording droplets becomes inferior, and in some cases, the disabled discharge of recording droplets may take place particularly when the heater power is made smaller.
As described above, no ink jet recording head has been developed to make a high quality printing possible by discharging small droplets at higher frequency.